The present invention provides a rechargeable electric storage battery comprising oppositely charged graphitic carbon electrodes that have been simultaneously intercalated by either charge-transporting positive ions or negative ions contained in the same electrolyte. Such a battery is believed to provide reasonably high power density and energy density characteristics, fabrication simplicity, a relatively long lifetime, and potential economic advantages.
Although intense research is currently yielding new battery systems, these alternatives to conventional lead-acid batteries often suffer from serious drawbacks.
A galvanic cell wherein both electrodes consist of electron acceptor intercalated graphite compounds and the electrolyte is a solid fluoride ion conductor is disclosed in "Novel Graphite Salts of High Oxidizing Potential", Ph.D. thesis of Eugene M. McCarron, III, Lawrence Berkeley Laboratory, University of California, Materials and Molecular Research Division, August, 1980, at page 125. These electrodes undergo the following electrochemical reactions: EQU SbF.sub.5 .multidot.IG+F.sup.- +e.sup.+ .fwdarw.SbF.sub.6 .multidot.IG, at the anode; and, EQU SbF.sub.6 .multidot.IG+e.sup.- .fwdarw.SbF.sub.5 .multidot.IG+F.sup.-, at the cathode,
where IG denotes intercalated graphite, e.sup.- denotes an electron, e.sup.+ denotes a hole. However, because both graphite electrodes are intercalated with electron acceptor compounds, this leads to disappointingly low observed voltages of 0.4-0.5 V.
Graphite has also been intercalated anodically through oxidation from highly concentrated strong acids such as H.sub.2 SO.sub.4 and HSO.sub.3 F. See, Bottomley et al, Journal of the American Chemical Society, 1963 at page 5674; and, Besenhard et al, Carbon, v. 18, pp. 399-405 (1980). No intercalation at the cathode is reported in these works.
U.S. Pat. Nos. 3,956,194 and 4,041,220 disclose electrochemical generators wherein the anode consists of an alkali metal, the cathode comprises alkali metal intercalated into an electron acceptor intercalated graphite compound, and the electrolyte may be a solid alkali metal or an organic solvent. The following electrochemical reactions occur at the electrodes: EQU Na.fwdarw.Na.sup.+ +e.sup.-, at the anode; and, EQU Na.sup.+ +FeCl.sub.3 .multidot.IG.fwdarw.NaFeCl.sub.3 .multidot.IG+e.sup.+, at the cathode,
where IG, e.sup.-, and e.sup.+, are defined as before. As with prior art batteries wherein the anode is an alkali metal and the cathode is an electron acceptor intercalated graphite compound (see, e.g., U.S. Pat. Nos. 4,052,539 and 4,119,655), these battery systems suffer from disadvantages inherent in the use of an alkali metal as an electrode. Such disadvantages include the substantial absence of the ability to be recharged, and inherent safety hazards.
It is now known that certain doped polymers such as polyacetylene and polyphenylene can be employed as electrodes in socalled organic batteries. (See, e.g., U.S. Pat. No. 4,321,114.) However, polyacetylene is extremely sensitive to air, and both even when doped possess very low current carrying capabilities which require the use of a current carrying support backing.
In contrast to the aforementioned prior art electric storage battery systems, the battery provided by the present invention is not only rechargeable, but exhibits enhanced charge storage capability, uncomplicated electron-ion exchange kinetics, stability during the charge-discharge cycle even at elevated temperatures, fabrication simplicity, a relatively long lifetime, and potential economic advantages.
According to the present invention, a battery with highly satisfactory physical properties is produced by simultaneously intercalating two oppositely charged graphitic electrodes from the same electrolyte.
It is an object of the present invention to provide an electric storage battery wherein no solids are deposited and redissolved during charge-discharge cycles.
It is an object of the present invention to provide an electric storage battery wherein the graphitic electrodes provide their own structural and conductive integrity without the need for support backing.
It is a further object of the present invention to provide a process for the production of an electric storage battery having oppositely charged graphitic electrodes simultaneously intercalated by charge-transporting anions and cations contained in the same electrolyte.
These and other objects and advantages will be apparent to those skilled in the art from the following detailed description and appended claims.